The central objective of this research program on population and quantitative genetics is to characterize the nature and extent of genetic variation in populations and the forces and their interplay which lead to the maintenance of this variation. Research efforts are of a basic investigative nature and general in scope. They are directed at the construction of theoretical models and development of their consequences into verifiable predictions, and concurrently, at the accumulation and interpretative analysis of information obtained both by field observations and laboratory experimentation with natural populations. A major effort is directed at isozyme variation: extent and pattern of variation and covariation in natural frequency compositions in experimental populations, biochemical properties, and mutation rates. Related studies are aimed at the development and experimental testing of mutant polygenes with small deleterious effects. Analytical tools are being developed and evaluated in all phases of the research. Principally, experimental research is conducted with Drosophila and maize.